* Run in same container
* Add cross compile targets to makefile
* Use make targets and existing container
* Cache UI build
* Update cross-compile script
The toolchain is already bundled in the stashapp/compiler image.
Rather than introducing a second one via GH actions standardize on that
one instead.
Also
* Clear up what "Cross Compile" actually does
* Still pull stashapp/compiler separately for easier debugability.